Processing circuits and other electronic circuits generally require direct current (DC) voltages that are stable and free of transients. Accordingly, the processing circuits and other electronic circuits need to be electrically connected to power supplies that are stable and free of transients. Transients and other variations in the DC power supplies can cause the processing and other electronic circuits to experience anomalies or failures.
High speed and large scale processing circuits are very susceptible to problems caused by voltage variations. Some of these voltage variations are caused by load transient currents and other variations in the DC power supplies. Transient currents react with inherent inductance to create voltage variations, wherein the voltage variations are proportional to the inductance and the derivative of the current over time.
Processing circuits rely on very precise, high speed clock signals to control data signals that pass throughout the processing circuit. The clock and data signals are voltages that are in either a logical xe2x80x9chighxe2x80x9d state, a xe2x80x9clowxe2x80x9d state. Transient currents (sometimes referred to herein simply as xe2x80x9ctransientsxe2x80x9d) on the DC power supplies can cause the clock and data voltages to be falsely interpreted by the receiving circuits as high or low. An erroneously or falsely interpreted clock signal results in the improper flow of data throughout the processing circuit, which may cause the data signals to be improperly processed. An erroneously or falsely interpreted data signal results in an improper data value being processed.
As processing circuits become faster, their clock signal frequencies and the load transient currents increase. In addition, the magnitude of the clock operating voltages decreases. For example, a high frequency clock may use a voltage of 1.3 volts. The increased frequencies of the clock signals result in a decrease in the periods that the clock and data signals are in either the high states or the low states. This limited period at a given state, coupled with a lower operating voltage, increases the criticality of voltage variations on the clock operating voltage. Thus, a very small voltage variation is able to force a clock or data signal into the wrong state. Accordingly, a processing circuit using a high frequency clock is very susceptible to errors caused by relatively small transients and other voltage variations in the DC power supplies. Without very well regulated and stable DC power supplies, the clock speeds and, thus, the processing capabilities of processing circuits are limited.
One method of reducing transients on the power supplied to a processing circuit is by physically locating the power supply close to the processing component, or components, of the processing circuit. This close proximity reduces the distance of the conductors between the power supply and the processing component, which in turn reduces the inductance of the conductors. The length of a conductor is often referred to as the net length. The reduced net lengths reduce inductance and, thus, voltage variations are reduced.
Locating the power supply physically close to the processing component, however, creates additional problems that degrade the performance of the processing circuit. For example, the close proximity of the power supplies to the processors forces other components, such as memory interface circuitry, remote input/output interface circuitry, crossbar communication circuitry, and clock distribution circuitry, to be placed farther away from the processors and, thus, creates performance bottlenecks in each of these varied, yet important computer subsystems. For example, memory components may have to be located a greater distance from the processing component. Accordingly, the net lengths associated with these components increase. The increased net lengths increases the latency between the processing component and its associated components, which slows the processing circuit. For example, a component may require several cycles of the clock in order to respond to a signal received from the processing component.
Other problems occur when the power supply and the processors are located in close proximity to each other. For example, both the power supply and the processing component generate relatively large quantities of heat. When the power supply is physically located near the processing component, a high density of heat is created in the vicinity of the processing component. This heat adversely affects the processing component, i.e., high-temperatures negatively affect silicon transistor switching times and severely degrade the operational frequency of the processor. Adequately removing the heat requires the use of relatively sophisticated and expensive cooling systems, such as refrigerated or cryogenically cooled systems. These cooling systems increase the cost and complexity of the processing circuit as well as decreasing the reliability of the processing circuit.
One method of overcoming the problems of component density and routing resources in processing circuits is to have separate printed circuit board assemblies for the processing and memory subsystems. The separate subsystems, however, compromise the performance of the processing to memory interface. Latency across multiple connectors and multiple boards is high, and bandwidth is reduced. Accordingly, the highest attainable performance is not able to be achieved.
The above-described problems have limited the capabilities of processing and other electronic circuits. Therefore, a need exists for a processing circuit that has a reduced susceptibility to voltage variations and that has processing components located within close proximity to each other.
A circuit comprising multiple circuit boards is disclosed herein. An embodiment of the circuit may comprise first and second printed circuit boards. The first printed circuit board may comprise first and second conductive planes. The first conductive plane has a first shape and the second conductive plane has a second shape, wherein the first shape is substantially similar to the second shape. The first conductive plane is located adjacent the second conductive plane, wherein the first conductive plane is parallel to and aligned with the second conductive plane. The second printed circuit board is connected to the first printed circuit board.